Stent having adjacent elements connected by narrow flexible webs

ABSTRACT

A stent and method of making incorporating flexible, preferably polymeric, connecting elements into the stent wherein these elements connect element(s) across an intervening space. The polymeric connecting elements are designed to fold within the space between the outer diameter of the stent and the inner diameter of the stent.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation under 35 U.S.C. § 120 of U.S. patentapplication Ser. No. 15/865,579, filed Jan. 9, 2018, which is acontinuation under 35 U.S.C. § 120 of U.S. patent application Ser. No.14/801,486, filed Jul. 16, 2015, now U.S. Pat. No. 9,895,243, issuedFeb. 20, 2018, which claims the benefit of provisional 62/025,670, filedJul. 17, 2014, all of which are incorporated herein by reference intheir entireties.

FIELD OF THE INVENTION

The present invention relates to the field of implantable stents havingflexibly connected adjacent structural elements.

BACKGROUND OF THE INVENTION

The use of implantable stents in the vasculature and other body conduitshas become commonplace since first proposed by Dotter in the 1960s.These devices are required to have a small, compacted diameter forinsertion into an intended body conduit and transport, typically via acatheter, to a desired site for deployment, at which site they areexpanded to a larger diameter as necessary to fit interferably withluminal surface of the body conduit. Balloon expandable stents areexpanded by plastically deforming the device with an inflatable balloonon which the expandable stent was previously mounted in the compactedstate, the balloon being attached to the distal end of the catheter andinflated via the catheter. Self-expanding stents are forcibly compactedto a small diameter and restrained at that diameter by a constrainingsleeve or other means. Following delivery to a desired site fordeployment, they are released from the restraint and spring open tocontact the luminal surface of the body conduit. These devices aretypically made from nitinol metal alloys and typically rely on the superelastic and biocompatible character of the metal. Nitinol stents thatrely on the shape memory attributes of that material are also known.

The evolution of implantable stents has also included the use of atubular covering fitted to the stent, either to the outer surface, theluminal surface or to both surfaces of the stent. These covered stentshave generally come to be referred to as stent-grafts. The coverings aregenerally of a polymeric biocompatible material such as polyethyleneterephthalate (PET) or polytetrafluoroethylene (PTFE).

It is also known that stent graft coverings may be optionally providedwith perforations if desired for particular applications. Because of theopen area provided by the perforations, such devices having perforatedcoverings may be considered to be a sort of hybrid stent andstent-graft, as are devices that include stent frames having metallicstent elements or structure and polymeric elements connecting, coveringor other otherwise being attached to the stent elements. The presence ofthe polymeric elements reduces the otherwise open space between theadjacent metallic stent elements, either very slightly or verysubstantially depending on the intended application and mechanicaldesign.

Generally, a fully covered stent-graft can be considered to have asurface area (hereinafter A_(max)) equal to the outer circumference ofthe expanded stent multiplied by the length of the stent. For aconventional, open frame stent (as opposed to a stent-graft), thesurface area represented by all of the stent elements is only a smallportion of the maximum surface area A_(max). The actual surface areacovered by the stent, meaning the area covered by all components of thestent (including flexible connecting elements and graft coveringmaterial) in their deployed state, is A_(stent). The porosity index, orP.I., describes the open area (the portion of the maximum surface areanot covered by all components of the stent assembly) as a percentage ofmaximum surface area, wherein:

P.I.=(1−(A _(stent) /A _(max))).times.100%.

One method of measuring the actual surface area covered by the stent(A_(stent)), involves the use of a machine provided by VisiconInspection Technologies, LLC (Napa, Calif.). The Visicon Finescan™ StentInspection System (Visicon Finescan machine model 85) uses a 6000 pixelline scan camera to generate a flat, unrolled view of a stent. TheVisicon Finescan also has an updated model, the Visicon Finescan Sierrathat exists and may be used alternatively to measure actual surfacearea. In operation, the stent is mounted on a sapphire mandrel with afine diffuse surface. This mandrel is held under the linear array cameraand rotated by the system electronics and is used to trigger the lineararray camera to collect a line of image data in a precise line-by-linemanner. After a complete revolution an entire image of the stent isacquired. When the entire stent has been imaged, the softwaredifferentiates between the stent with cover and the background. Thetotal number of picture elements (pixels) is compared to the totalnumber of pixels associated with the stent and cover to determineA_(stent). Basic settings on the machine used for this type ofdetermination are (for example): light, 100%; exposure, 0.3 ms/line;gain, 5; threshold, 50; noise filter, 20; smoothing, 4.

The open area may be a continuous single space, such as the spacebetween windings of a single helically wound stent element. Likewise theopen area may be represented by the space between multiple individualannular or ring-shaped stent elements. The open area may also berepresented by the total area of multiple apertures provided by either asingle stent element or by multiple stent elements providing multipleapertures. If multiple apertures are provided they may be of equal orunequal sizes. The use of a perforated graft covering or of polymericelements in addition to metallic stent elements may also reduce the openarea.

Stents having a porosity index of greater than 50% are considered to besubstantially open stents.

In addition to the porosity index, the size of any aperture providingthe open area must be considered if it is intended to cover only aportion of a stent area for a specific stent application. For multipleapertures, often the consideration must be for the largest size of anyindividual aperture, particularly if the apertures are to provide for a“filtering” effect whereby they control or limit the passage of biologicmaterials from the luminal wall into the flow space of the body conduit.

A shortcoming of some stent devices that combine metallic stent elementswith flexible polymeric connecting elements is that the non-metallicelements, (e.g., polymer webs), when constrained circumferentially oraxially or when bent into a curved shape, may protrude into the luminalspace of the device. This type of protrusion into the luminal space ofthe device may create opportunities for clinical complications such asstenosis, thrombus, altered blood hemodynamics, and associatedcomplications.

In light of the foregoing, there is an ongoing need for endoprosthesessuch as stents or stent grafts that when deployed have sufficient radialforce, porosity, and flexibility, while having minimal impact to bloodhemodynamics and other clinical complications typically associated withinterfering structures of a medical device. The embodiments describedherein provide a flexible endoprosthesis (e.g. a stent or stent graft)with potentially less interference into the luminal space than currentlyknown devices.

SUMMARY OF THE INVENTION

An endoprosthesis is described having a length, a radius, an innercircumference and an outer circumference, the endoprosthesis comprisingadjacent stent elements having spaces there between, the adjacent stentelements including multiple apices with multiple flexible connectingelements that extend across the spaces between the adjacent stentelements, wherein the flexible connecting elements are biased to foldsubstantially between the inner circumference and the outercircumference when the endoprosthesis is compacted. Folding of theflexible connecting elements is the result of the application of alongitudinal (axial) or alternatively a bending force applied to theendoprosthesis. The phrase “folded flexible connecting elements” thusdescribes the bent shape of the flexible connecting elements resultingfrom the application of such forces. Prior to the application of suchforces, the flexible connecting elements are typically substantiallystraight between their attachment points to the stent structure Theflexible non-metallic connecting elements or measured webs with anaverage width to thickness ratio of less than 10 (as transversely at themiddle of the length of the web) provide a stent with flexibility,useful resistance to forces that may be applied to the device in vivosuch as torsion forces, bending forces, axial tension or compression, orradial compression, and minimize encroachment of portions of the deviceinto the luminal or abluminal space.

Another embodiment provides an endoprosthesis having a length, a radius,and a circumference, the endoprosthesis comprising adjacent stentelements having a space there between, the adjacent stent elementsincluding multiple apices wherein one apex of a stent element isconnected across the space to a pair of apices on the adjacent stentelement wherein the flexible connecting element has a section modulusM_(r) in a direction aligned with the radius of the endoprosthesis (i.e.as measured along an imaginary line extending perpendicularly through alongitudinal axis of a substantially tubular device) and a sectionmodulus M_(p) aligned in a direction perpendicular to M_(r) of theendoprosthesis (i.e. in a direction tangential to a circumference of asubstantially tubular device); and wherein M_(r)/M_(p)>0.2.

In one embodiment the endoprosthesis may be fabricated from a length ofserpentine, helically wound wire wherein the helically wound wireprovides the general cylindrical form of the endoprosthesis and whereinthe serpentine form of the wire provides sequential apices along thelength of the wire with each sequential apex pointing towards alternateends of the endoprosthesis. It is noteworthy that while theendoprosthesis may be fabricated from a single length of helically woundserpentine wire, the adjacent windings of the helically wound wireconstitute the adjacent stent elements with spaces there between asreferred to above. Helically wound stent frames are inherently unstablein absence of a secondary linkage, such as a flexible connectingelement, connecting adjacent stent elements across intervening spaces.Utilization of the described flexible connecting element to interconnectadjacent rows stabilizes the helical structure and limits axialelongation, torsion and bending while allowing a high degree offlexibility.

Other stent forms such as multiple, individual spaced-apart ring-shapedstent elements may also be used. Ring shaped stent elements may be inthe form of zig-zag elements creating a circumferential ring, orinterconnected elements that provide diamond shaped openings in acircumferential sequence when the device is diametrically expanded.Alternatively, embodiments presented that utilize the helically woundserpentine forms are preferred for many applications. The stent ispreferably self-expanding (made from materials such as nitinol) but mayalso be made from materials suitable for balloon expandable stents(e.g., stainless steel, magnesium based alloys, magnesium, cobaltchromium alloy, titanium or titanium based alloys). The stent may alsobe configured such that polymeric linkages may connect metallicstructure(s) circumferentially and/or longitudinally.

In addition to stents and stent-grafts, embodiments of theendoprosthesis described herein may be manufactured in suitable forms toserve as other diametrically expandable implantable articles for use invarious bodily conduits. These may include embolic filters, variousvascular occluders, vena cava filters, heart valve stents, etc.

Flexible connecting elements inherently provide flexibility to theendoprosthesis but also may have a tendency to fold into the lumen whencompacted (e.g. circumferentially, diametrically, axially,longitudinally, bending etc.). This folding of the flexible connectingelements into the lumen (when the endoprosthesis is constrainedcircumferentially or axially or when bent into a curved shape) can haveundesirable clinical responses. Manufacture of the flexible connectingelements as described herein can reduce the amount of folding of theflexible connecting elements into the lumen and therefore aid in a moredesirable clinical outcome.

The adjacent, spaced-apart stent elements are circumferentially orhelically oriented, meaning that they have a general direction oforientation perpendicular to the longitudinal axis of the stent, whenthe stent is in a straight, unbent state.

A method of making involves the application of a biocompatible polymericcovering to the chosen stent form to create, temporarily, a stent-graft.The covering is preferably of a strong and thin material and may be in atubular form, although sheet forms (e.g., relatively wide films cut intonarrow tapes, or wide films applied such that there is a seam linerunning longitudinally along the length of the endoprosthesis) arepreferred for manufacturing as will be described. The covering can beapplied to the outer surface of the stent, but may also be applied onlyto a luminal surface, or alternatively may be applied to both theluminal and abluminal (outer) surfaces of the stent. A covering isapplied so that a desired thickness of a flexible connecting element canbe achieved. The thickness of the flexible connecting element comparedto the width of the flexible connecting element aids in the folding ofthe flexible connecting element (when the endoprosthesis is constrainedcircumferentially or axially or when bent into a curved shape) to besubstantially within the outer and inner circumference of the metallicstructure. Covering both the luminal and abluminal surfaces allows forthe possibility of covering substantially all of the metallic surfacesof the stent with the desired polymer. The polymeric film covering insome embodiments comprises a thermoplastic film with strength propertiesthat result in relatively uniform directional shrinking properties whenthe film is subjected to heat above its melt point. The film-coveredstent graft may be provided with shaped apertures or partial apertures(slits or other puncture openings) through all or most of the thicknessof the film, such as at locations between adjacent stent elements, aswill be further described. The punctured stent-graft is then exposed toheat above the melt temperature of the film which causes the film toshrink back from the edges of the previously created puncture, resultingin openings through the wall of the stent. These openings are of size,shape, quantity and orientation that are a result of the size, shape,quantity and orientation of the previously created punctures, the amountof heat subsequently applied and the thickness and type of polymericfilm used. It is apparent that these are manufacturing variables thatmay be controlled as desired. The resulting open area of the stent(i.e., porosity index) may cover a wide range but typically will begreater than 50% and for example may be around 70% to 80%. The remainingpolymeric film following the heating step is in the form of polymericwebs extending across the space between adjacent stent elements, thesepolymeric webs thereby serving as flexible connecting elements betweenthe adjacent stent elements.

In various embodiments, the width and thickness of the flexibleconnecting element can be controlled. For example, the amount of filmapplied, (i.e., thickness), and/or the size of the slits or apertures,and/or laser settings, and/or by layering films having different heatretraction properties. For example, if two films having different heatretraction properties are layered together, and then slit and heatretracted, a transverse cross section of the resulting flexibleconnecting element may have a variable width through its thickness.

Further, the finished open frame stent may optionally be provided withanother, additional covering of polymeric graft material to create astent-graft if desired. This graft covering is easily adhered or bondedto the covering or coating that is provided over the stent elements(e.g., the wire) and forms the flexible interconnecting webs. Thiscovering may have different material properties that aid in strength oradhesion or carrying therapeutic agents. The cover may further then bepunctured to create a stent graft that has an axially strong linkage incontact with another layer of material that may provide as a carrier fora therapeutic agent.

The polymeric covering of these finished devices (that include amultiplicity of openings and a multiplicity of flexible polymericinterconnecting webs) is generally continuous or substantiallycontinuous between the stent ends, being the result of having been madefrom a continuous sheet of film or the result using helically wrappedpolymeric tape with overlapping adjacent edges that are melt-bondedtogether. The film covering that forms these continuous webs is welladhered to the stent elements.

In another embodiment, the polymeric covering is perforated along themetallic structure portion such that the metallic portion and thepolymeric covering would be exposed to the lumen wall. This allows thestent graft with the polymeric covering to have metallic anchoring tothe vessel wall. The area of the stent that has the polymeric materialremoved can be used as a reservoir for therapeutic agents. This removalprocess can be done with a laser. These reservoirs can then have anotherlayer of material spanning over the reservoir to create an enclosed orpartially enclosed pocket or a protective layer for the therapeuticagent. The vessels of the body typically adhere well to metalliccomponents, so by providing openings along the metallic frame (i.e.polymeric material is removed) the stent graft has anchor points wherethe body can adhere the stent to the vessel. In addition, these openingscan act as anchor points along the stent and provide stop points for adeployment system such as a deployment system described in U.S. Pat. No.6,224,627 to Armstrong et al. that may allow for a more controlleddeployment.

In another embodiment, the section modulus (M_(r)) may vary along alength of the flexible connecting element spanning an opening betweenadjacent stent elements. The varying section modulus (M_(r)) can providereservoirs for therapeutic agents. The varying section modulus can alsoprovide for “stop points” (i.e. a discontinuity in the flexibleconnecting element located at selected positions along the length of thestent structure (e.g. the wire)) These stop points may provide for amore controlled deployment by creating a location that a constrainingcovering can rest or stop against during a deployment.

In another embodiment, a flexible connecting element (i.e., “linkage”)may be further tailored to optimize side branch and main branch luminalhemodynamics. The hemodynamics may be improved by tailoring of thelinkage cross sectional geometry. For example, a 0.003 inch (0.0762 mm)thick linkage has a lower volume of a stagnation zone (e.g. bloodentering into or exiting from a side branch of the major stented vessel,or simply the character of the blood flow immediately adjacent to theluminal surface of the endoprosthesis) than a 0.002 inch (0.0508 mm)thick linkage, but a more optimized linkage thickness may be in therange of 0.005 inch (0.127 mm) and 0.010 inch (0.254 mm). Also, anarrower linkage may improve hemodynamics compared to a wider linkage.For example, a 0.020 inch (0.508 mm) wide linkage may be more optimizedthan a 0.100 inch (2.54 mm) wide linkage in relation to improvedhemodynamics. The hemodynamics can also be tailored by profiling orshaping of the cross section of the linkage. The linkage can have across section that is of varying shapes. These cross sections can beachieved by covering the stent in films that have different heatretraction rates. They can also be tailored by other means such as alaser. A linkage cross section can be shaped to deflect flow to adesired location. For example, in the venous system, a linkage may beprofiled to deflect flow from a side branch into the main branch.

In another embodiment, a flexible connecting element may be tailored tocreate stagnation zones or to limit the amount of flow that passes bythe linkage. One example of this use is if the device is to be used toexclude an aneurysm, the cross section is designed to create astagnation zone in the appropriate region of the aneurysm (e.g. todecrease aneurysm coagulation time).

In another embodiment, a flexible connecting element or linkage may becreated by using a material that has elastic properties. When thelinkage is made from a material that has elastic properties, a devicecan have longitudinal and circumferential expansion. This may prove tobe advantageous in a tortuous anatomy where the material or covering orlinkage can go into longitudinal tension on one side of a curved portionand longitudinal compression on another side of a curved portion, e.g.an opposite side. Another potential advantage is if the device has aclot or thrombus attached to it, the device can be circumferentiallydilated, by a balloon for example, to dislodge a clot or thrombus. Ifballoon dilation is relaxed the device can go back to its pre-dilateddiameter. A method of applying an elastic material to a stent is toapply the material in a stretched configuration up to the point ofplastic deformation.

In another embodiment, a connecting element may be made of a materialthat has elastic and non-elastic properties. For example, an elasticmaterial may be laid adjacent or on top of a non-elastic material or anon-elastic material may be laid adjacent or on top of an elasticmaterial. The materials may also be alternating through the thickness ofa linkage. One potential advantage to using elastic materials andnon-elastic materials on the same device is that it may be possible toachieve a longitudinally stiff device in tension (and when compressedlongitudinally the elastic portion folds substantially “in plane”) andan elastic device circumferentially.

In another embodiment, a linkage can have a reinforcement member createdto make a device more stiff when the device is constrained in diameter.Typically, the stiffness of a device is controlled by a metallicstructure of the device. For example, a wire diameter of the device canbe changed to change the amount of radial stiffness and it can betailored to a desired state. In present known devices, the larger thewire diameter, the stiffer the device. In some cases, a stiffer devicehas a tradeoff of less fatigue resistance. One way to combat thistradeoff, is to add a reinforcement feature to the linkage. Thisreinforcement feature may be metallic or non-metallic. It can be layeredinto the film when the films are being applied or applied after heattreatment of the polymer films. The reinforcement feature may also bemade by creating a densified region or a region that is stiffer than thepolymer web.

In another embodiment, a linkage may have an ingrowth layer applied toit. An ingrowth layer meaning a layer that allows ingrowth of the vesselinto the polymer covering. The ingrowth layer may be added after thelinkages have been created or it may be incorporated into the layeringof the films. The ingrowth layer may be embedded in the layers and thenexposed through a subsequent laser or other removal process.

Linkages that span the space between adjacent stent elements may take onvarious shapes and sizes. The linkage may have an undulating patternthat aids in the linkage folding substantially “in plane” and in somecases within the space between the outer and inner boundary of themetallic portion of the device.

Still further, these devices and linkages may be provided with coatings(e.g., elutable coatings) of various therapeutic agents (e.g., heparin)by various means known in the art that are suitable to the particularagent. Furthermore, these devices may be applied with hydrogels thatallow the linkages to change shape, e.g., by swelling. These hydrogelscan be applied to the entire device or strategically to certain linkagesby known methods in the art.

Stents made as described herein have good conformability enabled by theflexible interconnecting webs between adjacent stent elements thatprovide flexibility and anatomic apposition while increasing luminalspace by potentially minimizing material folding into the lumen. Inaddition they may allow for optimized blood flow passing through thelinkage. This optimization can be used to minimize stagnations in themain vessel and maximize stagnation in an aneurysm. Furthermore, theymay enhance the linkages and may create better clinical outcomes. Theyalso have good flexural durability enabled by interconnecting websbetween adjacent stent elements that mitigates fracture due to cycliclongitudinal bending in curved anatomies. The expandable device isscalable to accommodate a range of vessel sizes (e.g. 3 mm-55 mm).

Potential clinical applications of the expandable device describedherein include, but are not limited to: congenital defects (i.e.,pulmonary artery stenosis, aortic coarctation), adjunctive aortictherapy (i.e., Type I endoleaks; aortic side branch stenting),peripheral artery disease (i.e., renal and iliac artery stenosis,aneurysm, and dissection) and venous applications.

“In plane” is defined in the context of when the stent is substantiallyfully longitudinally (i.e. axially) compacted using manually appliedforce. In one embodiment, a fully longitudinally compacted stent withflexible connecting linkages can be observed when an apex of one windingis closer to the apex of an adjacent winding than the apices 22b of theadjacent winding. Under these circumstances, the characteristics of thelinkages being “in plane” is defined as the linkage orienting (e.g.folding) itself such that a substantial portion of the linkage length iswithin an outer circumference or boundary of one individual stentwinding and inner circumference or boundary of the same individual stentwinding.

“In plane” test method: Obtain a stent with flexible interconnectingwebs between adjacent stent elements. Obtain a mandrel with an outerdiameter approximately 2 mm smaller than the inner diameter of thestent. Insert the mandrel into the inner diameter of the stent so thatthe flexible interconnecting webs that are to be evaluated are outsideof the mandrel. Longitudinally compress the stent by up to the stent'smaximum longitudinal compression so the flexible interconnecting websare substantially limiting further longitudinal compression of the stent(e.g. see FIG. 8A). Visually evaluate the flexible interconnecting websto determine if the straight portion of the web is not significantlyfolded and if the web is substantially within the outer boundary andinner boundary of an individual stent winding that a given web isattached to.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B describe respectively a perspective view and a plan viewof a helically wound serpentine wire form (previously known) of a stentas described herein.

FIG. 2A is a photomicrographic side view of a portion of a helicallywound serpentine wire stent (previously known) provided with flexibleinterconnecting webs between adjacent stent elements.

FIG. 2B is a further magnification of a portion of a similar helicallywound serpentine wire stent in a relaxed or non-folded configuration(e.g. minimal longitudinal compression on the stent) provided withflexible interconnecting webs shown by FIG. 2A.

FIG. 2C is a perspective view of a stent in a relaxed or non-foldedconfiguration (e.g. minimal longitudinal compression on the stent) inaccordance with an embodiment described herein, wherein each singleopening shown has an arrow head shape and the connecting flexiblelinkages are substantially non-curved.

FIG. 2D is a plan view of a stent in accordance with an embodiment.

FIG. 2E is a plan view showing a configuration according to analternative embodiment.

FIGS. 3A-3C are transverse cross sectional views of a helically woundserpentine wire in stent form with a covering applied to the helicallywound serpentine wire.

FIG. 3D is a representation of a perspective transverse cross section ofa flexible connecting linkage with a M_(r)/M_(p) ratio >0.2.

FIG. 3E is a representation of a perspective transverse cross section ofa flexible connecting linkage with a M_(r)/M_(p) ratio <0.2.

FIG. 3F is a transverse cross sectional representation of a stentshowing the outer circumference and inner circumference of the stent.

FIG. 3G is a perspective view of adjacent stent elements and a flexibleconnecting linkage folded substantially “out of plane”.

FIG. 3H is a perspective view of adjacent stent elements and a flexibleconnecting linkage folded substantially “in plane”.

FIG. 3I and FIG. 3J show some alternative transverse cross sections of aflexible connecting linkage, both consistent with linkages shown in FIG.2C and FIG. 2D, and representing a M_(r)/M_(p) ratio >0.2.

FIG. 3K shows a transverse cross sectional view of a flexible linkagewith a reservoir embedded in the flexible connecting linkage.

FIG. 4 is a scanning photomicrograph of a multiaxial ePTFE film usefulfor making the described open frame stent.

FIG. 5A shows a perspective view of a partially completed stent providedwith multiple slits or openings to create enclosed apertures withislands of material remaining within the apertures that are part of theprocess of manufacturing device embodiments described herein.

FIG. 5B shows a perspective view of the partially completed stent shownin FIG. 5A with the islands of material removed that are part of theprocess of manufacturing device embodiments described herein.

FIG. 6 is a side view of previously known art wherein flexibleconnecting elements fold substantially outside the space located betweenthe outer surface of the metallic stent and the inner surface of themetallic stent, i.e. “out of plane”.

FIG. 7A is a perspective magnified photographic image of previouslyknown art in partial longitudinal compression showing how the flexibleconnecting linkages fold “out of plane”.

FIG. 7B is a perspective magnified photographic image of previouslyknown art at or near full longitudinal compression showing how theflexible connecting linkages fold “out of plane”.

FIG. 7C is a perspective magnified photographic image of previouslyknown art at or near full longitudinal compression showing how apices onone side of an individual winding are raised further away from thelongitudinal axis of the stent, by the prior art connecting linkage, incomparison to apices on the opposite side of the same individualwinding.

FIG. 8A is a perspective magnified photographic image of a stent inaccordance with an embodiment wherein the flexible connecting linkagesfold substantially “in plane” when the stent is in a longitudinallycompressive state and the linkages are significantly limiting thelongitudinal compression.

FIG. 8B is a perspective magnified photographic image of a stent withlinkages that fold “in plane” and where the apices on one side of anindividual winding are at substantially the same distance from thelongitudinal axis of the stent as the apices on the opposite side of thesame individual winding (as opposed apex height relationship shown inFIG. 7C of the prior art).

FIG. 9A is a plan view of a stent in accordance with an embodiment,wherein the flexible connecting linkage that covers the metallicstructure has a discontinuous portion only above a portion of themetallic structure.

FIGS. 9B-9G show transverse cross sections of the reservoir and themetallic structure.

FIGS. 10A and 10C are plan views of a stent in accordance with anembodiment, wherein the polymer webs have extensions covering a portionof the metallic stent structure. FIGS. 10B and 10D show a transversecross section of the web extensions along a length of the metallic stentstructure.

FIG. 11A is a plan view of a stent in accordance with an embodiment,wherein the polymer webs have a reinforcement section.

FIG. 11B is a plan view of a stent wherein polymer webs have analternative configuration of a reinforcement section.

FIG. 11C is a plan view of a stent in accordance with an embodimentwherein the polymer webs have an undulation when the stent is in arelaxed configuration (e.g. minimal longitudinal tension or longitudinalcompression being applied to the stent).

FIGS. 11D, 11E and 11F each show a plan view of a stent in accordancewith one embodiment wherein the stent has flexible connecting elementsmade up of an elastic portion and a non-elastic portion.

FIG. 12 is a side perspective view of a balloon expandable stent (or alength portion of such a stent) provided with flexible interconnectingwebs between adjacent stent elements.

FIG. 13 is a side perspective view of previously known art where threestent rings are shown without an interconnecting polymeric covering.

FIG. 14 is a side perspective view of a stent assembly, comprising thestent rings shown in FIG. 13, provided with an interconnecting polymericcovering

FIG. 15 is the upper left section of the stent assembly described byFIG. 14, shown as a perspective detail.

FIG. 16 is a side perspective view of a balloon expandable stent (or alength portion of such a stent) provided with flexible interconnectingwebs between adjacent stent elements.

DETAILED DESCRIPTION OF THE DRAWINGS

As generally described above, a variety of stent forms may be usefullyprovided including the flexible connecting elements taught herein. FIG.1A shows a perspective view of a stent 10 for use in various embodimentsas described herein. The stent 10 shown comprises a helical winding of alength of serpentine wire 18. Sequential windings of the helical woundserpentine wire 18 result in spaced-apart adjacent stent elements 12.The ends 17 of wire 18 may be secured by any suitable method (e.g.,welding) to the longitudinally adjacent helical winding. For clarity,stent 10 is shown with a mandrel 16 extending through and beyond bothends of the stent lumen, making the side closest to the viewer visuallyapparent while blocking the view of the side of stent 10 furthest fromthe viewer. Mandrel 16 is present only for clarity of visualization andis not a part of stent 10.

The helically wound serpentine wire 18 extends continuously betweenopposing ends of stent 10, wherein opposing apices 22 a and 22 b formedof wire bends of relatively small radii are interconnected by straightor relatively straight wire segments 24. The apices typically “point” indirections that are substantially parallel to the longitudinal axis 19of the mandrel 16 and the tubular form of the stent 10, with alternatingapices 22 a and 22 b pointing in opposite directions, that is, pointingto opposite ends of the stent. In the embodiments as shown by FIG. 1A,apices pointing in one direction (e.g., apices 22 a) are aligned along afirst common line while the apices pointing in the opposite direction(e.g., apices 22 b) are aligned along a second common line that isparallel to the first common line.

FIG. 1B shows a plan (or flattened) view of details of the serpentinewire form described by FIG. 1A; dimensions relate to the method ofmaking described below. Dimension 27 is considered as the height(amplitude) of adjacent opposing apices while dimension 28 is the widthof adjacent opposing apices. Dimension 29 describes one full period ofthe serpentine form. Wire diameter 25 and bend radius 26 of the apices22 may be chosen as appropriate. Substantially triangular spaces aredefined by a triangular boundary wherein two apices of the triangularspace are a 22 b apex and the other apex is a 22 a apex that islongitudinally distal of the 22 b apices. The 22 b apices point proximaland the 22 a apices point distal.

FIG. 2A is a side magnified photographic perspective image of previouslyknown art, showing a portion of the length of an open-frame stent 10wherein spaced-apart, adjacent stent elements 12 (e.g., two adjacentapices 22 a connected to opposing apex 22 b) are interconnected by apair of flexible polymeric webs 32. Guitar pick shaped openings 34 aregenerally defined by the form of helically wound serpentine wire 18 andflexible polymeric webs 32. FIG. 2B is a magnified photographicperspective image of previously known art wherein the enclosed openings34 are shown to be somewhat oval shaped. The openings are separated by apolymeric web 32 wherein the polymeric web 32 is made up ofsubstantially only a shaped section 201.

In various embodiments, a finished stent 60 can be created. A coveringcan be applied and modified to create alternative flexible linkageelements 32. For example, as shown in the photomicrographic plan view ofFIG. 2C and the schematic plan views of FIG. 2D, the polymeric coveringmay be formed into flexible linkage elements 32 associated with anarrowhead shaped opening 34. The opening 34 may be formed when the coveris modified (e.g. a slit or perforation and then optionally further heatretracted) to form the polymer webs 32. The opening 34 may have a firstend at least partially bounded by an apex 22 a (or 22 b) and another endopposite the first end at least partially bounded by another apex 22 a(or 22 b). The opening 34 may be bound by five concave shaped sections(201, 216) and one convex shaped section 202 as viewed from within theopening 34. Four of the concave shaped sections 201 may be at least aportion of one of the webs 32 bounding the opening 34 and one of theconcave shaped sections 216 may be an apex 22 a or 22 b or a vestigialedge 36 associated with an apex 22 a or 22 b. The convex shape 202 asviewed from within the opening 34 may be an apex 22 a or 22 b (oppositethe apex 22 a or 22 b associated with the concave curved section 201) orassociated with apex 22 a or 22 b (e.g. vestigial edge 36). The opening34 may have a first end and a second end opposite the first end and oneof the ends has a concave shape 216 and the other end has a convex shape202 as viewed from within the opening 34. Alternatively, the opening 34may have a first end and a second end opposite the first end and one ofthe ends has a concave shape 216 and the other end has a convex shape202 and two concave shapes 201 as viewed from within the opening 34.

As shown in FIG. 2D, interconnecting elements 32 have a web centerline204 through the center of the length of an individual, randomly selectedweb (i.e., extending between the adjacent wire apices joined by thatweb). The web centerline 204 may form an angle 205 of between 15 and 75degrees with respect to a parallel line 203 with the web centerline 204of the stent (or parallel with the centerline 19 of mandrel 16 shown inFIG. 1). Said otherwise, for this type of stent with elementsinterconnected by flexible webs 32, the webs 32 may be oriented at anangle to the length of the stent. The web centerline 204 can also beconsidered a line of symmetry for the polymer web 32 for the portion ofthe web 32 that spans the space between adjacent stent elements 12. Thepolymer web 32 has a web length 208. The web length 208 is the distancebetween wire 18 on one stent element 12 and wire 18 on an adjacent stentelement 12 along the web centerline 204. In previously known stents, aweb length 208 is approximately three times its width 300. According toone embodiment the web length 208 is at least 5 times its width 300 andin another embodiment the web length 208 is 10 times its width 300.

Furthermore, as shown in FIG. 2D, the web 32 has a straight section 200and a curved section (or concave section as viewed from within opening34) 201 and the curved sections merge tangentially into the stentelement or a vestigial edge 36 along the stent element. The enlargedportion of FIG. 2D shows how these flexible polymeric webs 32 aregenerally straight until the web transitions from a straight section 200to a curved section 201 and the curved section 201 is joined to andattached to stent element 12 (e.g. via the vestigial edge 36). The webs32 are shown to have substantially straight sections 200, with astraight section length 207, and substantially curved sections 201wherein the straight sections 200 span more of the distance across aspace between adjacent stent elements 12 than the curved section 201.Curved sections 201 can be symmetrical about a centerline 204 or theycan be unsymmetrical. The straight section 200 is narrower than thecurved sections 201, but alternatively the straight section 200 may bewider than a curved section 201 as shown in FIG. 2E.

In various embodiments described by FIGS. 3A-3C, a stent has atransverse cross section across a wire 18. For example, a finished stentwith a covering that has been applied, slit, and heat retracted can havea transverse cross section with a vestigial edge 36 when the coveringhas been applied to either the outer or inner surface of the stent asshown in FIG. 3A. The stent may have a transverse cross section with acovering on the inner and outer surfaces of the stent 60 and havevestigial edges 36 as shown in the embodiments described by FIG. 3B andFIG. 3C.

In various embodiments, a web 32 has a cross section 302 with anassociated section modulus. For example, as shown in FIG. 3D, thepolymeric web 32 from FIG. 2D, has a width 300 and a thickness 301 andan associated section modulus. The section modulus calculation forarectangular cross section is calculated as

${SectionModulus} = \frac{{Moment\_ of}{\_ Intertia}}{y}$

where y is equal to the distance from the centroid of the cross section302 to an outer edge. In the case of a rectangular cross section, thesection modulus can be generally simplified to

$\frac{{base\_ x}{\_ width}^{2}}{6}.$

In the radial direction the section modulus can then be calculated as,

${Mr} = \frac{{{width}(300)}{{xthickness}(301)}^{2}}{6}$

and in the perpendicular direction the section modulus is calculated as

${Mp} = {\frac{{{thickness}(301)}{{xwidth}(300)}^{2}}{6}.}$

The width 300 is the maximum distance of the cross section 302 of theweb 32 in the perpendicular direction. The thickness 301 is the maximumdistance of the web 32 in the radial (i.e. as measured along animaginary line extending perpendicularly through a longitudinal axis ofa substantially tubular device) direction of the section 302. Section302 is in a direction perpendicular to the straight section 200. Atransversely cut cross section 302 may be taken at the middle of thelength of the web 32 in any suitable fashion whereby the dimensions ofthe web are not deformed by the sectioning (e.g. cutting) process. Thesubsequent measurement of the dimensions of the transverse cross section302 may be accomplished using conventional scanning electron microscopymachine.

In various embodiments, a web can have a M_(r)/M_(p) ratio. For example,a web 32 may have a M_(r)/M_(p) ratio >0.5, but can also have aM_(r)/M_(p) ratio >0.2 and still fold substantially “in plane”. TheM_(r)/M_(p) ratio that allows for in plane bending or folding can changeas the web angle 205 of the polymer web changes. For example, as the webangle 205 as shown in FIG. 2D approaches zero degrees from a line 203running longitudinally through apices 22 a, the M_(r)/M_(p) ratio mayneed to be closer to 1 in order to fold substantially in plane with alongitudinally compressed device. As the polymer web angle 205approaches 90 degrees from the longitudinal line 203 throughlongitudinally adjacent apices 22 a and a web center line 204, theM_(r)/M_(p) ratio may also need to be closer to 1 for acircumferentially reduced device. The geometry of the web angle 205 canhave an effect on what the M_(r)/M_(p) ratio needs to be. In oneembodiment, the polymer web angle 205 is oriented at approximately 45degrees from a line 203 running longitudinally through apices 22 a andthe desired M_(r)/M_(p) ratio is greater than 0.5. Previously knowndevices have a M_(r)/M_(p) ratio less than 0.2 and ratios less than 0.2tend to have more folding into the lumen.

Perspective transverse cross sectional views of the flexibleinterconnecting elements 32 are shown in FIG. 3D and FIG. 3E. Web 32 mayhave a square or rectangular cross section 302. A square or rectangularcross section 302 can have neutral axes 305, 305′ and 305″. The neutralaxes 305, 305′ and 305″ can be calculated by known means. Neutral axis305 can be considered a longitudinal component of the neutral axes. Aweb width 300 of the web 32 that may be used in a section moduluscalculation is measured along neutral axis 305′ where 305′ is aperpendicular component of the neutral axes. A web thickness 301 of theweb 32 that may be used in a section modulus calculation is measuredalong neutral axis 305″ where 305″ is a radial component of the neutralaxes. FIG. 3D is a representation of a cross section 302 that has aM_(r)/M_(p) ratio greater than 0.2.

FIG. 3E shows a perspective view of a transverse cross section ofpolymeric web 32 from FIG. 2B of previously known art. The width 300 ofthe web 32 is typically much wider than the thickness 301 and thesection modulus ratio M_(r)/M_(p) is less than 0.2. When the sectionmodulus ratio M_(r)/M_(p) is less than 0.2, the linkages may have agreater tendency to fold more towards the luminal or abluminal space andout of the space defined by the inner circumference and outercircumference of the stent. In previously known devices the linkagewidth can be greater than 20 times the thickness and often is more onthe magnitude of 50 times the thickness. The alternative webs describedherein typically have widths less than 20 times the thickness. In analternative embodiment, the width may be less than 10 times thethickness. In another alternative embodiment, the width may be less than4 times the thickness. In still other alternative embodiments, the widthmay be less than the thickness. The width to thickness ratios requiredfor “in plane” folding, may change depending on the angle 205 of the web32 with respect to the centerline of the stent, or the length 208 of theweb 32.

FIG. 3F shows a transverse cross sectional view of an entire finishedstent 60. “In plane” is defined as being substantially within the spacebetween an outer circumference 60′ or boundary and inner circumference60″ or boundary of the stent 60. “Out of plane” is defined as beingsubstantially outside the space between the outer circumference 60′ andinner circumference 60″. Folding of a linkage may occur when the stentis compacted, e.g. circumferentially, diametrically, axially, bending,or longitudinally. One way of determining if the linkage folds “inplane” or “out of plane”, is longitudinally compact the stent byapproximately 20%, and evaluate if the linkage is substantially “inplane” or “out of plane” by the above definition.

FIG. 3H shows a perspective view of a web 32 shown in FIG. 3D attachedto adjacent stent elements 12 with a M_(r)/M_(p) ratio greater than 0.2.The stent has been compacted and the web 32 is shown to foldsubstantially “in plane”.

FIG. 3G shows a perspective view of a previously known web 32 shown inFIG. 3E attached to adjacent stent elements 12 with a M_(r)/M_(p) ratioless than 0.2. The stent has been compacted and the web 32 is shown tofold substantially “out of plane”.

In various embodiments, polymer webs 32 have transverse cross sections302, that may have different shapes, including but not limited tonon-rectangular. For example, as shown in FIG. 3I the cross section 302can have a triangular shape. The web 32 with the triangular crosssection can be used for various purposes. For example, it could directflow from a side branch vessel into a main branch vessel or from a mainbranch into a side branch. The transverse cross section 302 has neutralaxes (305,305′, and 305″) and can be calculated by known means. Theneutral axis 305 is a longitudinal component of the neutral axes(305,305′, 305″). A web width 300 of the web 32 to use in a sectionmodulus calculation is measured along neutral axis 305′ where 305′ is aperpendicular component of the neutral axes. A web thickness 301 of theweb 32 to use in a section modulus calculation is measured along neutralaxis 305″ where 305″ is a radial component of the neutral axes. In analternative embodiment, the cross section can be hour glassed shaped asshown in FIG. 3J. In other embodiments, the cross section 302 can be ofother shapes not explicitly shown.

FIG. 3K shows a cross section 302 that has a reservoir 310 in a polymerweb 32. Polymer web 32 can be made to have a ratio M_(r)/M_(p)>0.5 evenwith the reservoir 310 in the polymer web as shown. The reservoir 310can be made by laser cutting as described herein or other known methods.The laser cutting process can be tailored to create an area of adhesion311 in the bottom of the reservoir 310. The reservoir side 312 is theside formed after laser cutting a reservoir 310 that is partiallythrough the thickness of the polymer.

While various polymeric films may be suitable for use as the stentcovering (or coating) material for this device, combinations of FEP(fluorinated ethylene propylene) films used in combination with ePTFEfilms are described herein. The ePTFE films described herein for usewith these helically wound serpentine wire stents are films havingmultiaxial fibrillar orientations as shown by the scanning electronphotomicrograph of FIG. 4. It is seen how the fibrils are oriented inall directions within the plane of the ePTFE film. ePTFE films of thistype may be made as taught by U.S. Pat. No. 7,306,729 and US PublishedPatent Application 2007/0012624 to Bacino et al. Films of this same typemay optionally be provided with a partial covering of a thin layer ofFEP (having openings through the FEP film covering; i.e., adiscontinuous covering). FEP coated ePTFE films, with either adiscontinuous (porous) FEP covering (coating) or a continuous(non-porous) FEP covering (coating) may be made generally as taught byU.S. Pat. No. 5,735,892 to Myers et al.

While, as noted, various types of films may be used for the stentcovering, the described ePTFE films has a multiaxial (within the planeof the film) strength orientation. It is strong, thin, and has excellentbiocompatibility. When suitable heat is applied following slitting, thefilm will retract (shrink back) with good uniformity to create theopenings 34 through the polymeric stent covering and to create theflexible polymeric interconnecting webs 32 between adjacent stentelements. Different films or films with different heat retractioncharacteristics can be stacked on top of each other or layered such thatthe film retracts to form cross sections such as those shown in FIG. 3Iand FIG. 3J.

FIGS. 5A and 5B show a partially finished stent 13 of helically woundserpentine wire 18 provided with a first outer (abluminal) covering ofFEP film and an additional covering of multiaxial ePTFE film, whereinapertures 41 (e.g., multiple continuous slits to form a triangleenclosure) have been made through the film between adjacent apices ofthe wire that are pointed in the same direction. In some embodiments,after the film has been slit, forming the apertures or triangularenclosures as shown, islands 504 of the ePTFE film can be left behind asshown in FIG. 5A. These islands 504 can be removed, (e.g. by using avacuum device) and thus forming larger openings 41 as shown in FIG. 5Bprior to heating the film. Heat can then be applied to the device havingapertures 41, causing the film(s) to shrink back toward the adjacentwire stent elements, subsequently resulting in the openings 34 in afinished stent 60 as shown in FIG. 2C.

A method of making a flexible stent is as follows. A stainless steelmandrel of diameter equal to about the inside diameter of the intendedstent is obtained. The mandrel surface is provided with exterior groovesto accommodate and locate the structural elements of the stent. In oneembodiment such as shown, for example, in FIG. 2D the stent hasamplitude 27 of 0.108 inches (2.743 mm) and a wavelength 29 of 0.124inches (3.150 mm). The amplitude 27 is the distance from a distal apex22 a of one stent element 12 to the distal apex 22 a of an adjacentstent element 12 where the two distal pointing apices 22 a are pointingin the same direction. The straight segment 24 of the stent 10 in oneembodiment is 0.153 inches (3.886 mm) approximately. A shallow groovemandrel has grooves wrapped in the same pattern as the stent was wound,but at a depth of 0.002 inches (0.0508 mm) compared to a larger depth,e.g. 0.0024 inches (0.061 mm) that is used for the stent windingprocess. The depth of the shallow groove mandrel depends on the wirediameter of the stent but fora 0.012 inch (0.305 mm) to 0.018 inches(0.457 mm) wire, a depth of 0.002 inches (0.0508 mm) deep is acceptable.In this case, a 12 mm diameter mandrel was used with a 0.012 inch (0.305mm) diameter wire and a 0.002 inch (0.0508 mm) deep shallow groovemandrel is used. A stent of the desired length and diameter made ofhelically wound serpentine nitinol wire is provided (wire diameter asdesired). This is then wound around the surface of the shallow groovemandrel such that the stent is sitting in the grooves and the apices ofthe serpentine wire are aligned so that apices pointing in a commondirection are aligned with and parallel to the longitudinal axis of themandrel. The end of the stent wires are secured to an adjacent windingof the stent wire using an FEP thread tied with a securing knot. Thestent is then helically wrapped with a covering of a single layer of FEPtape that has been cut from FEP film (0.00015 inch thickness or 0.0038mm and about 0.75 inch width or 19.05 mm), and stretched tightly overthe outer surface of the stent with minimal overlap of adjacent edges ofthe FEP tape. This FEP tape is then cigarette wrapped (wrapped in adirection perpendicular to the longitudinal axis of the mandrel) with anePTFE film of the type described previously. This wrapping may bestarted by aligning a transverse edge of the film with the longitudinalaxis of the mandrel and attaching it to the underlying FEP film bycarefully melt-bonding the ePTFE film edge to the FEP using a heatsource such as a clean soldering iron or appropriate equivalent. Twelvelayers of the ePTFE film are wrapped around the outer surface of thestent and the film edge is trimmed along the length of the stent (i.e.,parallel to the longitudinal axis of the mandrel). The film edge issecured with the previously used heat source.

As shown in FIGS. 5A and 5B, shaped apertures, or openings 41, arecreated between adjacent wire apices that are pointed in the samedirection. These apertures 41 may be created by any suitable means,including the use of a scalpel blade, water jet, laser, etc. One suchsuitable laser is a Coherent Inc., Model: GEM-100A, CO.sub.2, CW(continuous wave only), Santa Clara, Calif. The size of these shapedapertures 41 is dependent on the desired width 300 of the flexibleconnecting element 32. The laser cut aperture 41 was cut in a triangleshape such that legs 501 and 502 (after retraction at least a portion ofthe legs 501 and 502 become the vestigial edges 36) of the triangle wereoffset from the straight portions or segments 24 of the wound stent by0.030 inches (0.762 mm) and the circumferentially oriented remaining leg500 (after retraction at least a portion of leg 500 can become shapedsection 202) was offset a distance 505 of approximately 0.031 inches(0.787 mm) from the adjacent apical tangent line 503. After the heatretraction step the width of the linkage was approximately 0.007 inches(0.178 mm) wide and approximately 0.003 inches (0.076 mm) thick. Thisallowed for the linkage to fold substantially in plane with aM_(r)/M_(p) ratio >0.4. The width and thickness of the polymer web 32can be further tailored to make the web 32 closer to a M_(r)/M_(p)ratio >0.5. The thickness 301 of the linkage 32 may be in the range of0.002 inches (0.0508 mm) to 0.004 inches (0.102 mm) but may inalternative embodiments be in the range of 0.0005 inches (0.0127 mm) to0.007 inches (0.178 mm). The width of the linkage 300 may be about 0.007inches (0.178 mm), but can alternatively be in the range of 0.003 inches(0.076 mm) to 0.022 inches (0.559 mm). The last row of apices at eachend of the stent may be omitted from apertures if it is desired to leavethese end rows covered in their entirety (i.e., in stent-graft fashion).The entire length of the wrapped stent is then provided with a temporaryhelical wrap of Kapton® Polyimide Film tape (Dupont, 0.002 inch or0.0508 mm thickness); the ends of this tape may be secured to thesurface of the mandrel beyond each end of the stent with a mechanicalclip or other temporary fastener. This layer of Kapton is then tightlywrapped with a temporary helical wrap of ePTFE tape (made from an ePTFEfilm having a fibrillar microstructure with fibrils orientedpredominately parallel to the length of the tape and wrapped with asmall pitch angle so that the orientation is primarily circumferentialwith respect to the mandrel). This ePTFE tape will providecircumferential compression to the underlying materials when suitablyheated.

The above construction can then be placed into a suitable convectionoven set at 370 degree C. for 17 minutes, after which it can be removedfrom the oven and allowed to cool to approximately ambient temperature.As one of ordinary skill in the art can appreciate, the times andtemperatures can be varied slightly to achieve desired results. Theouter layers of ePTFE film and Kapton tape are then removed. Theresulting coated stent and underlying layer of Kapton tape are thencarefully removed from the mandrel. Remaining film edges protrudingbeyond the ends of the stent may then be carefully trimmed in atransverse direction close to the end apices of the stent wire with ascalpel blade.

FIG. 6 is a schematic side view of a previously known stent 15 as itwould appear mounted on a balloon (not shown) for subsequent deploymentand expansion where the webs 32 are bowed or wrinkled, and “out ofplane”, when previously known stent 15 is foreshortened.

FIG. 7A shows a magnified photographic image (approximately 13×) ofpreviously known device in a partially longitudinally compressed statewith a M_(r)/M_(p) ratio <0.2 and the webs fold substantially luminallyinward and consequently folding out of plane (i.e., are folded inward tothe extent that they extend inward beyond the space defined between theouter and inner circumferences of the stent). The webs tend to stay inthis configuration as long as a compaction force is applied. In thiscase, the compaction force was a longitudinally applied force thatshortened the overall length of the stent.

FIG. 7B shows a magnified photographic image of a previously known stentin substantially a fully longitudinally compressed state with thelinkages folding out of plane. FIG. 7C is another view of the stentshown in FIG. 7B showing how the apices of an individual winding are atdifferent distances from the longitudinal axis of the stent, whichappears to be a result of the linkages folding out of plane duringlongitudinal compression of the stent.

FIG. 8A shows a magnified side photographic image (approximately 8×) ofa stent with a M_(r)/M_(p) ratio >0.2 in a partially longitudinallycompressed state where the webs 32 fold substantially “in plane”. FIG.8B is a magnified photographic image of a substantially fullylongitudinally compressed stent with linkages or webs foldingsubstantially in plane. The opposing apices 22 a and 22 b of any oneindividual winding are substantially at the same distance from thelongitudinal axis of the stent. This phenomenon can be largelyattributed to the linkages folding in plane.

In various embodiments a reservoir 90 can be formed in a covering (e.g.ePTFE) along a metallic structure (e.g. wire 18). For example, as shownin FIG. 9A, a reservoir 90 can be formed into the ePTFE covering alongthe serpentine wire 18 of a stent. The reservoir 90 can be through thefull thickness of the ePTFE covering or partially through the thickness.If the reservoir 90 is through the full thickness versus partiallythrough the thickness, the stent frame is exposed. The reservoirs cantake on various shapes.

In various embodiments, a stent may have a reservoir 90 along a wire 18and the stent may have a wire and polymer reservoir cross section 91.For example, as shown in the transverse cross sections B-B of FIGS.9B-9G from FIG. 9A, the wire and polymer reservoir cross section 91 hasa reservoir side wall 92. The reservoir sidewall 92 can have variousangles 95 with respect to a center line or plane 93. For example, asshown in FIG. 9B, the sidewall 92 has an angle between 0 degrees and 90degrees. The sidewall 92 may alternatively have an angle of zero degreesas shown in FIG. 9C. The sidewall 92 may also have an angle greater than90 degrees. The sidewall 92 may have multiple angles, for example someare greater than 0 degrees and some are less than 0 degrees with respectto the vertical perpendicular plane 93, and substantially create anarcuate shape 96 as shown in FIG. 9D. The side walls 92 may have angles95 less than zero degrees as shown in FIG. 9E. Furthermore, thesidewalls 92 may be configured as a continuous sidewall to create anarcuate shape 96 with respect to a center line 93 where the sidewall 92is concave as shown in FIG. 9F. The sidewalls 92 could also be convex.Other shapes and combinations of these shapes mentioned can also bemade. In various embodiments, a reservoir 90 can be covered. Forexample, as shown in FIG. 9G, an additional layer or covering 97 can beapplied along the stent 10 to create an enclosed reservoir 98. Thecovering may also be permeable or impermeable. If permeable it canslowly release an agent.

In various embodiments, a covering or a polymeric web 32 can have webextensions 100 and be discontinuous along a metallic structure such as awire 18. For example, as shown in FIG. 10A the web 32 has an extension100 that may extend beyond the shaped portion 201 along a wire 18. Theextension 100 has a length 103 that may extend along the wire 18. Invarious embodiments the extension 100 has a sidewall 101. As shown incross section C-C in FIG. 10B, the sidewall 101 may be perpendicular toa vertical plane or line 94. Furthermore, as shown by example in FIG.10C, the web extension 100 can have a nose cone shape. As shown in crosssection D-D in FIG. 10D, the sidewall 101 may have an angle 99 inrelation to vertical plane 94. The extensions 100 can be created bylaser removing the covering or by an etching process. These extensions100 can provide sufficient attachment of the web 32 to the stent 10while also providing an additional location on the stent frame for othermaterial or therapeutic agents or for creating adhesion zones 102 (thearea of the exposed stent frame that is between adjacent web footextensions 100). The adhesion zones 102 can be the exposed stent frameor the exposed stent frame can be treated by known methods to allow forbetter vessel attachment or be treated for any desired clinicalresponse. These adhesion zones 102, can act as “stop points” or alocation for a constraining covering to rest or stop against (e.g.during a deployment).

In various embodiments, a web or metallic structure may have an addedreinforcement section. For example, as shown in FIGS. 11A and 11B, web32 has added web reinforcement section 110. The web reinforcementsection 110 can be an added on piece such as a metallic section thatattaches or snaps onto the web 32 as shown, or it can be attached in anyother means including using an adhesive. The web reinforcement section110 can alternatively be a part of the polymeric web 32 wherein aportion of the web is densified or cured by any means including a laser.For example, the web may be densified along a straight portion 200 ofthe web 32. Web reinforcement section 110 can be attached before orafter the heat retraction step mentioned above in this document. The webreinforcement section 110 can be of any dimension, to get desired webstiffness, but a metallic reinforcement section can be used in a rangeof 0.0005 inches (0.0127 mm) to 0.010 inches (0.254 mm) equivalentdiameter.

The web reinforcement section 110 in FIG. 11A is shown on one side ofthe polymer webs 32. Alternatively, the reinforcement section 110 mayalso be on an opposite side such that the reinforcement section 110 ison two sides of the polymer web 32 and the reinforcement sections 110are in two distinct apertures 34 as shown in FIG. 11B. The webreinforcement sections 110 can also be used to reinforce mainly theshaped portion (e.g. curved) 201 of the polymer web 32 as shown in FIG.11B, but may also reinforce the straight portion 200. The reinforcementfeature 110 may also be along a vestigial edge 36 along an apex 22 a.The reinforcement feature 110 can be located just distal of apex 22 aand follow the contour of an opening 34. It may follow the entire insideboundary of the opening 34 or it may only partially follow the boundary.The reinforcement feature 110 can be incorporated to the wire 18 througha via located in the vestigial edge 36. If a vestigial edge 36 does notexist, the reinforcement feature 110 can attach directly to the wire 18.A web reinforcement may alternatively be along a web length 208 and maybe deposited on the web 32, e.g. a metallic coating that is sputtered orvapor deposited on or by other known means.

In the case where the reinforcement feature 110 is made out of a polymerthat is similar to the polymer web, the reinforcement feature can have adifferent density or porosity such that there is a distinct line that isvisible between the web 32 and the reinforcement feature. The distinctline or interface can be viewed under a Scanning Electronic Microscope(SEM). The reinforcement feature can be made by laser adjustments orother known methods. FIG. 11A and 11B show various configurations andshapes of the reinforcement section 110 and are not intended to belimiting as to what the configurations can be.

The reinforcement section 110 can be advantageous if an increase inradial stiffness is desired but fatigue resistance is of concern.Previously known designs increase the diameter 25 of wire 18 or increasethe metallic stent structure wall thickness to increase radialstiffness. A potential trade off to increasing the wall thickness orwire diameter is a decrease in fatigue resistance. This web modificationis a potential way to increase radial stiffness without decreasingfatigue resistance and perhaps, depending on the design, withoutincreasing profile.

In various embodiments, a polymer web may have a tortuous path along alength when the stent is in a relaxed configuration. For example, asshown in FIG. 11C, the polymer web 32 can have a tortuous path along itstortuous length 206 where an individual edge 120 has at least twoconcave shapes 124 and one convex shape 122 (as viewed from within theopening the edge borders) and the opposite edge 120′ has at least twoconvex shapes 122′ (e.g. a mirror image along centerline 204, of theconcave shape 124) and at least one concave shape 124′ (e.g. a mirrorimage along centerline 204, of the convex shape 122). The tortuous pathmay be along the centerline 204. The centerline 204 may be drawn as aline of symmetry along web 32. The undulating shape of the polymer web32 may aid in creating polymer web 32 that folds substantially with inthe outer diameter of the stent and the inner diameter of the stent,i.e. “in plane”. The edge 120 is along the polymer web 32 that spans thespace between the adjacent stent elements 12. The edge 120 is distinctfrom the vestigial edge 36. The undulating polymer web 32 has a tortuouslength 206 as measured along web centerline 204 that is longer than astraight, or non-undulating web, would have in the approximate sameposition. The length 206 is the distance along web 32 (e.g. the distancealong the symmetric centerline 204 spanning between adjacent stentelements 12). A tortuous length 206 in some cases may be 10% longer ormore than if the centerline 204 was straight and did not follow thetortuous path.

In various embodiments, a polymer web may have an elastic and anon-elastic portion. For example, as shown in FIG. 11D, the polymer web32 has an elastic portion 136 and a non-elastic portion 138. In thisembodiment, the web 32 connects between an apex of one winding toportions of the stent on either side of an apex on an adjacent winding.The elastic portion 136 is oriented such that the elasticity or stretchis oriented in a circumferential direction, i.e. a circumferentialcomponent, and the non-elastic portion 138 is oriented in a longitudinaldirection, i.e. a longitudinal component. The elastic portion 136 andnon-elastic portion 138 overlap each other at an attachment zone 139.The non-elastic portion 138 may extend in a longitudinal direction toconnect an apex 22 a from one stent element 12 to an apex 22 a on anadjacent stent element 12 as shown in FIG. 11E. Alternatively and/oradditionally, the non-elastic portion 138 may extend in a longitudinaldirection to connect an apex 22 b from one stent element 12 to an apex22 b on an adjacent stent element 12 as shown in FIG. 11F. The elasticportion 136 may alternatively or additionally connect circumferentiallyadjacent apices 22 b or 22 a as compared to connecting circumferentiallyadjacent wire straight segments 24. In some cases there may be multiplelongitudinal components connecting longitudinally adjacent stentelements 12 between circumferentially adjacent stent elements 135. Insome cases it may be desired to have the circumferential componentnon-elastic and the longitudinal component elastic or a combinationthereof.

The elastic portion 136 can alternatively be oriented at an angle suchthat it is partially oriented in the longitudinal direction andpartially oriented in the circumferential direction. The elastic portion136 and non-elastic portion 138 intersect and are attached in anattachment zone 139 as shown in FIGS. 11D, 11E and 11F. A web with anelastic portion 136 and a non-elastic portion 138 may be useful whentrying to minimize folding of the web into the luminal space but stillmaintain longitudinal strength. The elastic portion 136 may retractwithout substantially folding when constrained circumferentially sothere is minimal to no folding within the luminal space, and thenon-elastic portion 138 is oriented longitudinally through the apices 22a and provides longitudinal strength and because of its narrower width,when the stent is compacted circumferentially for example, the elasticportion does not substantially fold along its length. The non-elasticportion 138 and the elastic portion 136 may have a M_(r)/M_(p)>0.2.

One method of producing a polymer web 32 with the elastic portion 136and the non-elastic portion 138 (as generally shown by FIGS. 11D-11F) isas follows. With provided stent as described herein, wrap non elasticfilm on entire stent as also previously described, and then selectivelyremove the non-elastic film, with a laser, for example, as describedpreviously, such that the only non-elastic material left is as shown bythe non-elastic portion 138. The non-elastic portion 138 may span theentire space between two longitudinally adjacent 22 a apices of adjacentstent elements 12. The non-elastic film can also cover the wire 18 or itcan not cover the wire 18 in the straight segments 24 of the stentframe.

The film can be heat retracted at this point in the process before theelastic film is applied. Next, if needed, wrap a layer of adhesive wherethe elastic portion is to be wrapped. The elastic film can be stretchedup to the end of its elastic zone, such that if the film was released itwould rebound back to its prestretched condition, and wrapped onto thestent in this stretched or a partially stretched state. The film can bewrapped in a helical direction or a circumferential direction ensuringthat an attachment zone 139 is created at the overlap of the elasticportion 136 and the non-elastic portion 138 exists. If desired, thentrim the elastic portion 136 where needed. Then heat treat the stentwith the elastic and non-elastic material at a temperature sufficient tomake the adhesive flow and adhere. If FEP is used, heat treat atapproximately 270C. Since the material is elastic, the elastic portion136 may extend circumferentially between circumferentially adjacentwindings 135. The elastic portion may connect the wire straight segments24 between circumferentially adjacent windings 135. The elastic portion136 can aid in circumferential strength and stability.

FIG. 12 shows a perspective view of a balloon expandable stent 60, as itappears following diametrical expansion with a balloon. The stent 60shown comprises rings 62 wherein the balloon-expanded stent elementsform multiple diamond-shaped openings 63 d; stent 60 is typicallycomprised of one or more of these rings 62. The individual rings 62 maybe constructed by any suitable means known in art but can be fabricatedfrom a laser cut tube. For clarity, only the side of the tubular stent60 closest to the viewer is shown. Stent 60 is provided with a polymericcovering 66, preferably of a flexible film. It is apparent how covering66 interconnects the multiple rings 62 to create stent 60, via webs 32that span the distance between apices 22 a and 22 b of adjacent rings62. The webs 32 have a M_(r)/M_(p) ratio greater than 0.2.

While various polymeric films may be suitable for use as the stentcovering (or coating) material for this device, combinations of FEP(fluorinated ethylene propylene) films used in combination with ePTFEfilms are an example of one combination. In one embodiment, an ePTFEfilm for this device is a uni-axial film having higher strength in onedirection, with the direction primarily aligned with the longitudinalaxis 61 of the stent prior to balloon expansion. This type of film issimilar to that described in U.S. Pat. No. 5,476,589. In anotherembodiment, the film can be modified with an application of adiscontinuous coating of FEP similar to that taught in U.S. Pat. No.6,159,565. As already mentioned, films may be of an elastic materialsuch that when the linkages are formed, the linkages can stretch andreturn back to the pre-stretched state. These linkages can be formedbefore any heat retraction process is completed.

The arrangement of stent rings 62 are shown in FIG. 13 without polymericcovering 66 as the rings 62 would appear prior to balloon expansion.Unexpanded stent rings 62 are cut to have openings 63 which becomediamond shaped openings 63 d when expanded (as shown in FIG. 12). Stentrings 62 are placed in proximity to one another with apices 22 a and 22b in a typical apex to apex alignment. It is apparent that the distancebetween adjacent rings 62 may be as desired.

FIG. 14 illustrates the stent rings 62 as shown previously in FIG. 13with the addition of interconnecting polymeric covering 66. Webs 32,each a portion of polymeric covering 66, are shown to interconnectadjacent rings 62. FIG. 15 is an enlarged detail perspective view of theupper left end of stent 60 described in FIG. 14.

In various embodiments, punctures or slits 68 can be formed into acovering 66. For example, as shown in FIGS. 14 and 15 the punctures orslits 68 are arranged in the polymeric covering 66 along a longitudinalaxis 61 of stent 60. FIGS. 13-15 show a multiplicity of openings 63 and64 formed between adjacent stent elements of stent rings 62. Slits orapertures 68 sized such as previously described through polymericcovering 66 are formed of size and shape such that webs 32 have aM_(r)/M_(p)>0.2. These slits or apertures 68 may be formed by variousmeans as previously described and the slits may go through the filmthickness or they may create pockets by only going partially through thethickness of the film. Slits 68 are formed through the polymericcovering 66 that covers openings 63 that extend between opposing apices22 a and 22 b (openings that are enclosed between the ends of each stentring 62). Alternate openings 64 that extend from the middle of thelength of each stent ring 62 and fully to the end of each stent ring 62(i.e. between radially adjacent apices 22 a and 22 a, and likewisebetween radially adjacent apices 22 b and 22 b) are also provided withslits through the covering polymeric material 66. These slits 68 extendlongitudinally between adjacent rings 62 and into the correspondingopening in the adjacent ring 62. These slits 68 collectively createindividual interconnecting webs 32. Slits 68 may be of width as desired;the width of a scalpel blade may be deemed sufficient even though thefigures show that width of slit 68 corresponding to the width of theunderlying stent openings 63 and 64.

The apices 22 a and 22 b of each ring 62 may be made to point toward oneanother as shown in FIG. 12 or may be arranged to be offset as shown inFIG. 16 (i.e. aligned peak-to-valley as shown in FIG. 16 as opposed tobeing aligned in peak-to-peak fashion as shown in FIGS. 1A through 2E,FIG. 5 and FIG. 12). The apices typically “point” in directions that aresubstantially parallel to the longitudinal axis 61 of the tubular formof the stent 60.

One method of making a stent such as a stent shown in FIGS. 12 through16 is as follows. Standard diamond pattern geometry stents can be lasermachined and electro-polished at Laserage Technology Inc, Waukegan, Ill.from a 316 LVM stainless steel tube measuring 4.19 mm diameter times.0.38 mm wall thickness. The stent then is exposed to a surfaceroughening step to improve adherence without degrading fatiguedurability performance. Plasma treatment of the stents performed priorto FEP powder coating for purposes of cleaning and reducing contactangle of the metal surface is beneficial. Plasma treatment performed ascommonly known in the arts is acceptable.

FEP powder (Daikin America, Orangeburg N.Y.) can be applied to the stentcomponent by first stirring the powder into an airborne “cloud” in astandard kitchen-type blender and suspending the frame in the clouduntil a uniform layer of powder was attached to the stent frame. Thestent component then can be subjected to a thermal treatment of 320degree C. for approximately three minutes. This causes the powder tomelt and adhere as a coating over the stent component. Each ring thencan be coated a second time while suspending it from the opposite endand placed in 320.degree. C. oven for 3 minutes then removed and allowedto cool to room temperature.

Seventeen layers of a thin ePTFE film provided with a discontinuouscoating of FEP as previously described can be wrapped around a stainlesssteel mandrel measuring approximately 3.43 mm. The film is applied withits high strength orientation parallel to the longitudinal axis of thestent and with the FEP side facing out. Individual stent rings then areplaced over the film tube and aligned. The stent rings then can bealigned apex to apex and separated evenly with a gap of about 2.5 mmbetween each ring to achieve an overall device length of about 40 mm. Anadditional seventeen layers of the same film can be applied aspreviously described except with the FEP side oriented down, toward theouter diameter of the stent.

The entire assembly can be wound with several layers of an ePTFE thread(Part # SO24T4, WL Gore, Elkton, Md.) to impart compressive forces tothe underlying construct. The assembly can be placed in 320 degree C.oven (Grieves, Model MT1000, The Grieve Corporation, Round Lake, Ill.)for approximately 40 minutes. The stent assembly is then removed andallowed to cool to room temperature. The over-wrap is then removed andthe slits are created, such that M_(r)/M_(p)>0.2, and excess materialcan be removed.

In addition to being directed to the teachings described above andclaimed below, devices and/or methods having different combinations ofthe features described above and claimed below are contemplated. Assuch, the description is also directed to other devices and/or methodshaving any other possible combination of the dependent features claimedbelow.

Numerous characteristics and advantages have been set forth in thepreceding description, including various alternatives together withdetails of the structure and function of the devices and/or methods. Thedisclosure is intended as illustrative only and as such is not intendedto be exhaustive. It will be evident to those skilled in the art thatvarious modifications may be made, especially in matters of structure,materials, elements, components, shape, size and arrangement of partsincluding combinations within the principles of the invention, to thefull extent indicated by the broad, general meaning of the terms inwhich the appended claims are expressed. To the extent that thesevarious modifications do not depart from the spirit and scope of theappended claims, they are intended to be encompassed therein.

We claim:
 1. An endoprosthesis having a length, a radius, an innercircumference and an outer circumference, the endoprosthesis comprising:adjacent stent elements formed of a first material; and a flexibleconnecting element formed of a second material different than the firstmaterial, the second material being a polymeric material and theflexible connecting element spanning across a space between adjacentstent elements; and wherein the flexible connecting element is biased tofold substantially between the inner circumference and the outercircumference of the endoprosthesis when the endoprosthesis iscompacted.
 2. An endoprosthesis according to claim 1, wherein theflexible connecting element further comprises a thickness and a widthand the thickness is greater than one tenth the width.
 3. Anendoprosthesis according to claim 1, wherein the endoprosthesis iscompacted radially.
 4. An endoprosthesis according to claim 1, whereinthe endoprosthesis is compacted axially.
 5. An endoprosthesis accordingto claim 1, wherein a portion of the endoprosthesis is compacted axiallyduring bending.
 6. An endoprosthesis according to claim 1, wherein thereare at least two connecting elements spanning the space betweenlongitudinally adjacent stent elements, defining at least two boundariesof an enclosed opening.
 7. An endoprosthesis according to claim 6,wherein the enclosed opening has a first end and a second end oppositethe first end and one of the ends has a concave shape and the other endhas a convex shape.
 8. An endoprosthesis according to claim 1, whereinthe stent elements are made from a continuous helical winding of wire.9. An endoprosthesis according to claim 1, wherein the flexibleconnecting element further comprises a length and a width, wherein thelength is at least five times the flexible connecting element width. 10.An endoprosthesis according to claim 1, wherein the flexible connectingelement further comprises a width and a thickness and wherein the widthis less than ten times the flexible connecting element thickness.
 11. Anendoprosthesis according to claim 1, wherein the flexible connectingelement further comprises a web extension with a web extension lengthand a web extension width.
 12. An endoprosthesis according to claim 11,wherein the web extension has a length and the flexible connectingelement further comprises a length and wherein the web extension lengthis less than the flexible connecting element length.
 13. Anendoprosthesis according to claim 1, wherein the flexible connectingelement has a varying section modulus Mr.
 14. An endoprosthesisaccording to claim 1, wherein the endoprosthesis further comprises areservoir.
 15. An endoprosthesis according to claim 1, wherein the firstmaterial is a metallic material.
 16. An endoprosthesis having a length,a radius, an inner circumference and an outer circumference, theendoprosthesis comprising: adjacent stent elements formed of a firstmaterial; a flexible connecting element formed of a second material, thesecond material being a polymeric material, the flexible connectingelement spanning across a space between adjacent stent elements; andwherein the flexible connecting element is biased to fold substantiallybetween the inner circumference and the outer circumference of theendoprosthesis when the endoprosthesis is compacted, wherein theflexible connecting element has a section modulus (Mr) in a directionaligned with the radius of the endoprosthesis and a section modulus (Mp)aligned in a direction perpendicular to the radius of theendoprosthesis, wherein Mr/Mp of the flexible connecting element isconfigured such that the flexible connecting element is configured tofold substantially within the inner circumference and the outercircumference of the endoprosthesis when the endoprosthesis is compactedlongitudinally.
 17. The endoprosthesis of claim 16, wherein the firstmaterial is a different material than the second material.
 18. Theendoprosthesis of claim 16, wherein Mr is a varying section modulus. 19.The endoprosthesis of claim 16, wherein the flexible connecting elementfurther comprises a web extension that attaches to one of the stentelements with a web extension length and a web extension width, theflexible connecting element further comprising a length, and the webextension length is less than the flexible connecting element length.20. The endoprosthesis of claim 16, wherein there are at least twoflexible connecting elements spanning the space between longitudinallyadjacent stent elements, defining at least two boundaries of an enclosedopening, the enclosed opening having a first end and a second endopposite the first end, one of the ends having a concave shape and theother end having a convex shape.